The present invention relates in general to an H-type ceramic resonator and more particularly to an H-type monolithic resonator of piezoelectric materials for, for example, an electro-mechanical filter.
An H-type ceramic resonator is known and has two portions or leaves which resonate in their lengthwise direction, and a connecting portion or leaf bridging the two leaves at their intermediate portion to form an H-shape, the connecting leaf being made of the same material, and has the same thickness, as the two resonating leaves. Electrodes are disposed on both upper and lower surfaces of the resonating leaves.
Many attempts have been made to develop the H-type ceramic resonator, but have not yet been successfully applied for a practical use. One of the reasons of it is that the conventional H-type resonators have a double humped transmission characteristic with a "ripple" of several decibels (dB), wherein the term "ripple" represents a difference in attenuation between a summit of a hump or peak of a transmission characteristic curve and a valley or trough positioned between the two humps, as illustrated by Rp in FIG. 2. A small ripple of 0.5 dB or less would be negligible, but a ripple of 1.0 dB and more makes it difficult to carry out a tracking adjustment at 455 KHz for an intermediate frequency filter such as for AM (amplitude modulation) radios. Moreover, the ripple produces a distortion in transmission to result in deterioration in tone of radio outputs.